Containers made of corrugated paperboard have long been used for shipping and storing a variety of bulk materials such as powders, tobacco, metal castings, plastic resins, peanuts and many other materials. Such bulk materials are typically poured or thrown into the container and shipped loose so that the packed materials "flow" about the interior of the container.
Since the total weight of a single loaded container may run as high as fifteen hundred (1500) pounds, the packing and shipping of bulk materials presents several unique problems. One problem is that the side walls of the container must be sufficiently rigid in the horizontal plane to withstand internal movement of the load. Stated in the parlance of the trade, the side walls must resist against bulging as a result of internal material flow. Another problem is that the side walls of the container must also be sufficiently rigid to permit stacking of one container on top of another. Stated in the parlance of the trade, the side walls must provide sufficient compression strength to prevent any deformation or collapse of the container when others are stacked upon it.
While various prior art containers have been developed in an attempt to solve these problems, the problems persist. For example, in an effort to increase both bulge resistance and compression strength, U.S. Pat. No. 3,910,482 to Bamburg et al. discloses a laminated container having an outer box with an intermediate liner and an inner liner, each layer being formed of corrugated paperboard. Yet because all paper absorbs moisture, a container manufactured according to Bamburg (as well as any other multi-layered containers) loses its rigidity when placed or kept in a humid environment for any significant period of time. Because a warehouse typically provides just such an environment, these containers often deform and collapse. As a result, the containers are destroyed and the contents stored therein damaged or contaminated.
Multi-layered containers are conventionally manufactured with corrugated paperboard having vertically aligned corrugations. The purpose of this vertical alignment is two-fold. First, vertical alignment of the corrugations makes it easier to fold the container about a vertical line and thus form the corners. Second, vertical alignment of the corrugations increases the compression or stacking strength of the container. However, there are problems with using paperboard having vertically aligned corrugations. The primary problem is that this alignment or the corrugations renders the side walls more likely to crease or take a "false score". A related problem is that a container formed with vertically aligned corrugated paperboard is more likely to experience side wall bulge.
Yet another prior art attempt to improve both stacking strength and bulge resistance has been to insert posts into the corners of the container. These posts are often formed of laminated paperboard, wood or some like rigid material. While corner posts are recognized to improve stacking strength in unit load containers (containers for appliances, machinery, etc.), they are ineffective when used in a bulk material container for many reasons. One reason is that the bulk material is often surrounded in the container by a bag or sack made of polyurethane. As the bulk material flows within the container, the posts are dislodged and will tear the polyurethane bag. In addition, because the bulk material will settle into the corners of the container while being packed, the very insertion of any corner post can tear the polyurethane bag. Yet further, movement of the bulk material upon shipment of the container can break or splinter a corner post. Once the bag is torn, the posts can and often do contaminate the bulk materials stored therein.
Yet other problems exist when corner posts are used. The posts, by their very presence, decrease the usable volume of space within the container. Because the corner posts are placed directly in the corner, it is not possible to collapse or "knock down" containers with corner posts. It is desirable, and in light of the costs associated with shipping containers from the manufacturer to an end user, necessary that a bulk material container be knocked down for delivery to a customer. When inserted posts are used, they must be shipped separately of the container so that the container can be knocked down for shipping. Thus, the corner posts cannot be pre-attached to the container by the manufacturer. As a result, an additional unnecessary set-up cost is incurred by the end user. Furthermore, an additional cost is recognized in the shipment and maintenance of an additional inventory of posts separate and apart from the containers themselves. All of these factors work to increase the cost of the end product in terms of labor, handling, materials and time. These factors further work to increase the cost of purchasing the containers as the customer must coordinate the purchasing, storing and matching of containers and corner posts.
Thus, the prior art has heretofore lacked a bulk material container having sufficient side wall rigidity in both the horizontal and vertical planes to provide a container with the desired bulge resistance and compression strength. The prior art has further lacked a one-piece integral container of such side wall rigidity that could be knocked down flat for shipment by the manufacturer and easily set up by the end user.